Oxygen atom transfer from a trans-Dioxoruthenium(VI) complex to nitric oxide

In aqueous acidic solutions trans-[Ru^VI(L)(O)₂] ²⁺ (L=1,12-dimethyl-3,4:9,10-dibenzo-1,12-diaza-5,8- dioxacyclopentadecane) is rapidly reduced by excess NO to give trans-[Ru(L)(NO)(OH)]²⁺. When ≤1 mol equiv NO is used, the intermediate Ru^IV species, trans-[Ru^IV species, trans-Ru^IV(L)(O)(OH₂)]²⁺ be detected. The reaction of Ru^IV(L)(O)(OH₂)]²⁺ with NO is first order with respect to [Ru^IV] and [NO], k₂=4.13 ± 0.21) × 10¹M^-1s^-1 at 298.0K. δH⁺ and δ S⁺ are (12.0 ±0.3)kcal mol^-1 and -(11 ±1)calmol^-1K^-1, respectively. In CH₃CN,δH⁺ andδS⁺ have the same values as in H₂O; this suggests that the mechanism is the same in both solvents. In CH₃CN, the reaction of [Ru ^VI(L)(O)₂]²⁺ with NO produces a blue-green species with λ_max at approximately 650nm, which is characteristic of N₂O₃. N₂O₃ is formed by coupling of NO₂ with excess NO; it is relatively stable in CH₃CN, but undergoes rapid hydrolysis in H₂O. A mechanism that involves oxygen atom transfer from [Ru^VI(L)(O)₂] ²⁺ to NO to produce NO₂ is proposed. The kinetics of the reaction of [Ru^IV(L)(O)(OH₂)]²⁺ with NO has also been investigated. In this case, the data are consistent with initial one-electron O^- transfer from Ru^IV to NO to produce the nitrito species [Ru^III(L)(ONO)(OH₂)]²⁺ (k ₂>10⁶M^-1s^-1), followed by a reaction with another molecule of NO to give [Ru(L)(NO)(OH)]²⁺ and NO₂^- (k₂=54.7M^-1s^-1). Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.